Piezoelectric crystal plate



Oct. 18, 1949. BAERWALD 2,485,132

PIEZOELECTRIC CRYSTAL PLATE Original Filed March 19, 1945 EQU|VAl F NT INVENTOR. HANS (3. BAERWALD ATT RNEY Patented Oct. 18, 1949 2,485,132 I I rmzosrso'rmc CRYSTAL rum;

Hans G. Baerwald, Cleveland Heights, Ohio, as-

signor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Original application March 19, 1945, Serial No. 583,477. Divided and this application April 10, 1948, Serial No. 20,175

3 Claims. (01. 171-327) This application is a division of. my application Serial Number 583,477, filed March 19, 1945, for Piezoelectric crystal plates, to which reference may be made for a complete discussion of the in? vention with respect to all crystal classes to which the invention is applicable.

This invention relates to cuts of piezoelectric crystals and more particularly to thickness-conness-controlled elastic shear vibrations by longitudinal electric fields and/or dielectric displacements;

2. No elastic and dielectric interaction of these shear modes with any. other modes of vibration exists;

3. These orientations are independent of the physical constants of any particular material belonging to one of the specified classes of crystallographic symmetry as well as of extraneous physical conditions such as temperature. For the purpose of this description, cuts with these three properties are called piezoelectric unconditionally pure thickness-controlled shear cuts.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In accordance with a feature of the invention. there is provided a piezoelectric thickness-controlled shear crystal plate cut from crystalline material selected from one of the following piezoelectric classes of cubic symmetry: T; Ta; the plate which is cut therefrom having a pair of planeparallel major faces which aresubstantially parallel to a crystallographic axis and which substantially bisect the angle between the other two crystallographic axes.

With respect to the drawing, the figure shows the orientation of a piezoelectrically active crystal plate having thickness-controlled unconditionally pure shear modes of vibration for a material of the classes T; Tu.

According to the arguments presented in the description in the parent application, several different unconditionally pure shear waves, apart from equivalent ones, are possible in the cubic system, However, only those with the exciting field perpendicular to a plane bisecting two crystal axes and motion parallel to the other axis are piezoelectrically excitable by longitudinal fields. In the class To these planes are also crystallographic planes of symmetry, in the class T, only even-rank planes of symmetry. This distinction is, however, of no importance for our case as the two classes are identical with respect to all physical properties associated with tensors up to the rank 4.

As in the angular neighborhood of any pure shear cut undesired elastic interactions are proportional to the square of an angular deviation only and, therefore, are practically eliminated throughout that neighborhood, moderate angular deviations cannot only be tolerated but may even be desirable if they lead to a slight improvement in the temperature coeflicients.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a piezoelectric thickness-controlled shear crystal plate: a plate cut from crystalline piezoelectric material of cubic symmetry, said plate having a pair of plane parallel major faces which are substantially parallel to a crystallographic axis and which substantially. biSect the angle between theother two crystallographic axes.

2. In a piezoelectric thickness-controlled shear crystal plate: .a plate cut from crystalline piezoelectric material of the class T, said plate having a pair of plane parallel major faces which are substantially parallel to' a crystallographic axis and which substantially bisect the angle between the other two crystallographic axes.

3. In a piezoelectric thickness-controlled shear crystal plate: a plate cut from crystalline piezoelectric material of the class Ta, said plate having a pair of plane parallel major faces which are substantially parallel to a crystallographic axis and which substantially bisect the angle between the other two crystallographic axes.

HANS G. BAERWALDr REFERENCES CITED Mason, Physical Review, vol. 70, pages 529-537,

I 1946. (Copy m Scientlilc Library.) 

